Commercial poultry growers raise thousands of birds in large poultry houses. Chickens raised for meat consumption are grown from small chicks to market weight in about 6 weeks when conditions in the poultry house are optimal. This includes adequate feed, water, temperature, and fresh air ventilation.
The poultry houses are relatively inexpensive to construct and operate. A typical house is several hundred feet long and 40 to 60 feet wide. When a flock of chicks is first placed in the house, the internal temperature needs to be about 90 F and there is minimal need for ventilation with outside air. As the birds grow, the internal house temperature is lowered regularly, reaching about 70 F by the 4th week. The need for ventilation air increases as the birds grow. Older houses used moveable curtains on the side of the houses to let in light and admit warm or cool fresh air during favorable weather conditions. The curtains could be closed to keep out undesirable weather and daylight or keep heat in the house.
Most modern houses have continuous metal side walls and rely on large fans and louvers for ventilation to remove humidity, carbon dioxide, and ammonia and move fresh outdoor air through the house. The inlet louvers of these modern houses are typically installed along the side walls near the eaves, and spaced roughly 30 to 50 feet along the length of the house. As the fans exhaust air from the house, fresh, outside air is pulled in through the inlet louvers.
During the fall, winter, and spring, the requirements to bring in fresh air into the house, result in cold air being drawn into the house. To maintain ideal temperature in the house to maximize bird growth, the growers will run heaters. The fuels used most frequently in poultry house heaters are propane and fuel oil, which are delivered by tanker truck to the houses. These are generally the most expensive heating fuels per unit of energy delivered. Less expensive fuels, such as natural gas, are not widely available to growers in rural locations.
In many parts of the United States, the cost of heating the poultry house is as much as one third of grower's variable costs of operating the house. Occasionally, due to conditions in the fuel markets or extreme weather, the reduced availability of fuel will cause the price of fuel to rise rapidly during the heating season. During those times, the growers may lose money on operating the poultry houses and in extreme cases, may not have adequate supplies to maintain the required temperatures in the houses to protect the birds.
An alternative to heating with propane and fuel oil is solar heating using solar thermal collectors. The solar heat that is available can be useful to displace some or all of the heat provided by the fuel burning heaters. Every unit of solar heat provided to the house displaces a unit of fuel based heat delivered from combustion of propane, fuel oil, or other fuel sources.
Typically solar collectors have been assembled from rectangular panels of about 30 to 40 square feet each, often called ‘black box’ collectors. The most common black box panels are used to heat water, but others heat air. The system is expensive to install due to the large number of manufactured panels and the numerous interconnections required between panels. Another solar approach is to install large, dark colored metal sheets on the wall and collect the solar heated air with fans and ducts from behind the metal sheets. This approach has been used on several large industrial buildings and is less expensive to install than the black box panels.
One disadvantage of the fixed metal sheet and smaller black box solar collectors is that they may be exposed to sunlight and generate heat during days with moderate temperatures, when no heating is required. Even when solar fans are not running, the collector surfaces are being heated and releasing heat by radiation, conduction, and by convection of warm air currents near the house, which adds heat to the house when it is not desired. Another disadvantage is that the fixed sheet metal collectors are generally more expensive then collectors made of thin flexible materials that can solar heat air with comparable efficiency. These flexible materials, produced in large rolls as polymer films, fabrics, and thin metal foils, can be combined to make efficient solar collectors at very low cost.
The current invention uses an alternate approach combining flexible materials to efficiently collect solar energy to heat air for use within poultry houses. The flexible materials are deployed in the form of a curtain attached to the side of the poultry house. The solar curtain takes advantage of technology familiar to many poultry growers and greenhouse growers to deploy a system that can be raised or lowered to take advantage of the solar and weather conditions to meet the heating needs of the poultry house.
The present invention combines 4 technologies common to the agriculture industry into a single innovative system to capture solar heat for poultry houses. Greenhouse film, allows sunlight to pass through the film while resisting UV degradation and resisting the passage of warm or cold air from outside the film. Agricultural shade cloth absorbs a portion of the solar energy that falls on the exposed face of the cloth, heating the cloth and the air that passes in close contact to it. Radiant barrier film reflects visible light and infrared energy and emits minimal energy from the shaded side. Greenhouse/poultry house moveable curtain technologies allow heating and insulating curtains to be raised or lowered to optimize the internal conditions based on outside conditions and provide heating and cooling energy savings.
The innovative combination of the 4 technologies in a single system can capture a significant amount of solar energy, in the form of solar heated air to heat poultry houses and can also keep the houses warmer by insulating the exterior wall from cold outside weather conditions. When rolled down along the side of the poultry house, the solar curtain creates a space between the side of the house and the side of the curtain facing the wall, helping to protect the house from cold winds and outdoor air temperatures, reducing the heat loss from the sides of the house caused by forced convection from the winds and conduction from the temperature differences between the outdoor air and wall along the warmer house sides. When the solar curtain incorporates a radiant barrier film, there is additional heat loss benefit in that during certain conditions, such as on cold nights, the radiant barrier will reflect heat from the warm house sides back toward the house side, thus preventing some radiant heat loss.
Another advantage of the preferred embodiment is that the solar curtain can be rolled up to reduce its exposure to the sun. This would typically occur during late spring, summer and fall, when no additional heating is needed in the poultry house. By rolling the curtain up to minimize its exposure, cooling breezes and nighttime radiation from the house sides to the surroundings, will help to cool the house. Rolling the curtain up, when not needed, will also reduce its exposure to solar energy, which would otherwise slowly degrade the fabrics and films of which it is composed. By rolling the curtain up, the life of the fabrics and films will be prolonged, extending its economic life before new films and fabrics would be installed.
Another preferred embodiment uses a shade cloth absorber fabric arranged in a corrugated fashion within the curtain. The corrugation of the shade cloth permits that air flowing through the shade cloth to come in contact with more than one portion of the solar heated shade cloth. Because the shade cloth has openings in its construction it allows air to pass through but it also allows a portion of the solar energy that falls on the curtain to pass through the cloth without impacting and heating the fabric. In commercial practice, shade cloth is often rated by the amount of sunlight that it will block from passing through the cloth from the front and out the back. A shade cloth rated at 60% will block 60% of the sunlight hitting the front from passing out the back of the cloth. Therefore the cloth will only absorb up to 60% of the solar energy falling on the front of the cloth. As a result, as air passes through the solar heated 60% shade cloth, there is only a maximum of 60% of the solar energy available at the solar heated cloth to heat the air as compared to a 90% shade cloth, which would absorb up to 90% of the solar energy falling on it. The lower heat energy transfer to the air of the 60% shade cloth compared to the 90% shade cloth, results in a lower heated air temperature leaving the 60% shade cloth for a given flow of air.
By passing air through a corrugated shade cloth with contact with more that one portion of the solar heated shade cloth, the air temperature exiting the second portion of the shade cloth will be higher than air passing through a single portion of shade cloth. Repeated passage through multiple portions of the corrugated shade cloth will continue to raise the air temperature, up to a practical limit for the leaving air temperature that is closer to a temperature approaching the shade cloth with no air flow, referred to as the stagnation temperature.
However, an advantage of using a shade cloth with lower shading rating, such as 60% shading, is that it allows air to flow more freely, with less pressure drop, than it would flow with a higher shading rating, such as 90% shading. Typically the 90% shade cloth is made with a tighter weave or thicker threads that result in less open space for sunlight or air to pass through the cloth. When air is forced through the tighter spaces in the higher rated shade cloth, such as when a fan pushes air through the cloth, it takes more fan energy to push air through the tighter spaces in the higher rated cloth than for air pushed through the lower rated cloth with more open space between threads. By balancing expensive electric energy required for the fan with the amount of heat energy gained by heat transfer from the shade cloth with varied ratings, will give the most economical solution for gathering solar heat from the curtain.
In another preferred embodiment, a radiant barrier film is installed within the curtain behind a lower rated shade cloth. The sunlight that passes through the shade cloth will be reflected back to the backside of the shade cloth by the radiant barrier film. For a 60% rated shade cloth, 40% of the solar energy would pass through the cloth and hit the radiant barrier. If 99% of that solar energy were reflected by the radiant barrier back to the shade cloth, which would absorb up to 60% of the reflected solar energy, another 23.7% (0.99×0.40×0.60) of the total solar energy hitting the curtain would be absorbed from the reflected energy hitting the backside of the shade cloth. So, the total solar energy absorbed would be up to 83.7% of the solar energy approaching the front of the curtain, instead of a maximum of 60% absorbed by a shade cloth with solar energy approaching only the front side.
There are several advantages to using the radiant barrier within the curtain. First, the radiant barrier results in higher solar energy absorbed by the shade cloth, compared to the use of a shade cloth of the same rating, without radiant barrier. Second, the use of the radiant barrier permits the use of lower rated shade cloths, with their advantage of lower pressure drop and fan energy use, without a loss of solar energy collection capability compared to higher rated shade cloths with higher air pressure drop and fan energy use. Third, the use of lower rated shade cloth also results in lower cost of the shade cloth compared to higher rated shade cloth with the same solar collections capability, as shade cloth typically increases with price as rating increases. Fourth, the use of the radiant barrier reduces the radiant heat loss from the warm walls of the warmer poultry house during cold days and nights when no solar heating is taking place, as the radiant energy from the warmer walls is reflected back by the radiant barrier toward the walls instead of passing through to the colder inner facing film, the shade cloth, and outer facing film of the curtain.